Sounds fine on the intensity => guardian-type mapping.
Good general idea on the antagonizer, but you can simplify it a bit: when the antagonizer is on, switch the sphere itself to the antagonized-dyson faction (PlanetFaction.SwitchToFaction(entity,otherFaction) or something like that), but don't do anything to the things already spawned, so they remain in the normal dyson faction. That should be all you need to do, though it may be that the normal faction code will need a small adjustment to handle the "dude, where's my dyson-sphere?" case.
The antagonized dyson faction could just be a subclass of the normal one, implementation wise, so you need very little code.